from datetime import datetime,timedelta


class ExpiredDict(dict):

    def __init__(self,expires_in_seconds):
        super().__init__()
        self.expires_in_seconds=expires_in_seconds


    def __getitem__(self, key):
        value,expiry_time = super().__getitem__(key)

        if datetime.now() > expiry_time:
            del self[key]
            raise KeyError("expired {}".format(key))
        self.__setitem__(key,value)
        return value

    def __setitem__(self, key, value):
        expiry_time=datetime.now()+timedelta(seconds=self.expires_in_seconds)
        super().__setitem__(key,(value,expiry_time))

    def get(self,key,default = None):
        try:
            return self[key]
        except KeyError:
            return default